1. Field
Embodiments relate to an electrophotographic image forming apparatus and an imaging cartridge.
2. Description of the Related Art
An electrophotographic image forming apparatus, which is applied to image forming apparatuses, such as a laser copy machine or a laser printer forms an image on a recording medium by forming a toner image on a photosensitive drum through the charging, light-exposure, and development processes, electrostastically transferring the formed toner image to the recording medium, and, lastly, fixing the transferred toner image to the recording medium.
In recent years, a demand for an electrophotographic image forming apparatus that forms an image of further high quality and has a further long lifespan has rapidly increased. For example, a high quality image may be formed by reducing a particle size of the toner (e.g., about 7 μm or less). In order to form a high glossy image, for example, a glass transition temperature (Tg) of the toner may be lowered. In the case of a polymerized toner, a lower Tg (e.g., about 58° C. or lower) is needed to facilitate low-temperature fixing and to obtain a high glossy image. Accordingly, a durability of the polymerized toner is weakening. Therefore, it is even more difficult to increase a lifespan of an image forming apparatus using a polymerized toner than it is difficult to increase a lifespan of an image forming apparatus using a pulverized toner. Thus, various technical problems need to be resolved to increase a lifespan of an image forming apparatus using a polymerized toner, and this includes preventing filming of a developing roller.
In the electrophotographic image forming apparatus, a supplying roller transfers toner from a toner reservoir to a developing roller. The developing roller transfers the toner to a photoreceptor drum. Also, the supplying roller also resets the developing roller by removing the remaining toner on the developing roller. In a conventional art, for example, a nip between the developing roller and the supplying roller is increased so as to prevent filming of the developing roller. For example, in a conventional art, resetting performance of the developing roller is enhanced by increasing hardness of foam of the supplying roller so as to prevent filming of the developing roller. Also, for example, in a conventional art, fouling resistance of the developing roller is enhanced by coating a surface of the developing roller with a coating solution including a resin having a low surface energy such as a fluorine resin so as to prevent filming of the developing roller, and thus a resetting performance of the developing roller is improved.
However, when the nip between the developing roller and the supplying roller is increased or hardness of the foam of the supplying roller is increased, a resetting performance of the developing roller improves, but stress applied to the toner increases. When the stress applied to the toner increases, for example, quality of the image may decrease as vertical white lines and high-tone dirty spots may be generated. When a surface of the developing roller is coated with a coating solution containing a resin having a low surface energy, such as a fluorine resin, a manufacturing cost may increase due to high expense of the fluorine resin. In addition, when a surface of the developing roller is coated with a coating solution containing a resin having a low surface energy, such as a fluorine resin, the use of a negatively chargeable toner may cause a reverse polarity toner, and thus problems such as background contamination may occur. Also, it is commonly known that filming of the developing roller is not significantly reduced even when a surface of the developing roller is coated with a coating layer including a resin having a low surface energy such as a fluorine resin.